Kuiper Quadrangle - Craters and Basins

Craters and Basins

Craters are ubiquitous features of the mercurian surface. For the purpose of mapping, a fivefold morphologic classification of craters (fig. 10 in McCauley andothers, 1981) is the basis for determining their relative ages. The youngest craters (c5) have sharp rim crests, textured ejecta blankets, and a well-defined field of secondary craters. Under favorable lighting conditions, the youngest craters exhibit bright rays superposed on all older materials. Older craters have increasingly degraded rims and lower relief and have lost their secondary crater fields. The major differences between mercurian and lunar craters are apparently related to the greater gravitational acceleration and the higher impact velocities on Mercury. Continuous ejecta deposits are less extensive, and secondary craters are more sharply defined and clustered nearer their primary crater. Also on Mercury, accentuated secondary craters form prominent crater chains radial to large craters.

Craters within the Kuiper quadrangle increase in complexity as they increase in size from simple bowl-shaped craters to complex craters with central peaks to multiringed basins. Kuiper (11° S., 31.5°) is a moderate-size crater with a central peak cluster; Brunelleschi (9° S., 22.5°) exhibits an incomplete ring of peaks; and Rodin (22° N., 18°) is a well-developed double-ringed basin. These three craters are mercurian counterparts in morphology to the lunar craters Copernicus, Compton (or Antoniadi), and Schrödinger. All craters larger than about 35 km diameter and basins are filled to some extent with plains materials, and exposed rims of partly buried craters within the basins indicate that the fill is about 700 to 1000 m thick (De Hon and Waskom, 1976).

Six basins ranging in age from cl to c3 were formed during the waning stages of high-impact flux when the surface was virtually saturated with craters and basins. Later cratering history records a decreasing impact flux: of craters larger than 50 km diameter, 42 are classed as c3; 19 craters are assigned to c4; and 9 craters are c5. There is also a decrease in the size of the largest crater or basin formed in each age class from c2 to c5.